Contamination control apparatus

ABSTRACT

The contamination control apparatus of this invention includes a hollow cabinet having a work area in one portion thereof and an opening therein permitting access to the work area from the exterior of the cabinet. Decontamination and air supply means are in the cabinet and positioned so that air discharge therefrom will be decontaminated and then passed into the work area. Diffusion means are mounted in the cabinet and positioned between the decontamination and supply means and the work area to facilitate the diffusion of the air as it enters the work area. Consequently, the air flows uniformly through the work area and assist in providing a clean air curtain over the access opening to the work area to facilitate the prevention of contaminated air from leaving or entering the work area through the access opening. A series of interconnected air plenum chambers are in the cabinet in communication with the work area, decontamination and air supply means, and the opening to the exterior of the cabinet to permit the air passing through the work area and a portion of air from outside of the cabinet to be directed to the decontamination and air supply means. Negative pressure reducing means are in the cabinet to direct a predetermined amount of decontaminated air out of the cabinet sufficient to maintain a lesser pressure within the cabinet and exteriorly thereof and, finally, air velocity indicator and control means are mounted on the cabinet to facilitate the control of air flow within the cabinet.

United States Patent 1191 Fowler, Jr.

[111 3,811,250 1451 May .21, 1974 CONTAMINATION CONTROL APPARATUS [75]Inventor: James McFarland Fowler, Jr.,

Albuquerque, N. Mex.

[73] Assignee: Bect'on, Dickinson and Company,

' East Rutherford, NJ.

1221 Filed: Apr. '25, 1973- 21 Appl. No.: 354,217

Related US. Application Data [60] Division of Ser. No. 208,454, Dec. 15,1971, which is a continuation of Ser. No. 839,967, July 8, 1969,

abandoned.

[52] U.S. Cl 55/274, 55/473, 55/DlG. 29,

98/ 115 LH [51] Int. Cl.....; B01d 31/00 [58] Field 61 Search 55/467;470-472, 55/473, 274, DIG. 29; 98/115 LH; 62/256; 73/212; 417/43 [56] IReferences Cited 3 Primary Examiner-Bernard Nozick Attorney, Agent, orFirm-Kane, Dalsimer, Kane,

Sullivan and Kurucz [571 9 ABSTRACT The contamination control apparatusof this invention includes a hollow cabinet having a work area in oneportion thereof and an opening therein permitting access to the workarea from the exterior of the cabinet. Decontamination and air supplymeans are in the cabinet and positioned so that air discharge therefromwill be decontaminated and then passed into the work area. Diffusionmeans are mounted in the cabinet and positioned between thedecontamination and supply means and the work area to facilitate thediffusion of the air as it enters the work area. Consequently, the airflows uniformly-through the work area and assist in providing a cleanair curtain over the access opening to the work area to facilitate theprevention of contaminated air from leaving orentering the work areathrough the access opening. A series of interconnected air plenumchambers are in the cabinet inacommunication with the work area,decontamination and air supply means, and the opening to the exterior ofthe cabinet to permit the air passing through the work area and avportion of air from outside of the cabinet to be directed to thedecontamination and air supply means. Negative pressure reducing means.are in the cabinet to direct a predetermined amount of decontaminatedair out of the cabinet sufficient to maintain a lesser pressure withinthe cabinet and exteriorly thereof and, finally, air velocity indicatorand control means are mounted on the'cabinet to facilitate the controlof air flow within the cabinet.

8' Claims, 6 Drawing'Fig ures minnow m4 3.811.250

SHEET 2 OF 4 F/G.Z

1 CONTAMINATION CONTROL APPARATUS BACKGROUND OF THE INVENTION Whenworking in a biological environment it is extremely advantageous toprovide means for controlling airborne contamination. In. addition tobeing able to control airborne contamination within the work area it isalso particularly usefulto provide easy access to the work area so thatnormal and efficient operation withinthe area can be carried out. So, itis valuable to the art to be able to contain the work area within aprotected atmosphere while simultaneously permitting easy access to thework area to carry out whatever functions are necessary within the area.Naturally, it is desirable to provide both protection againstcontamination from the exterior of the work area as well as protectionagainst contaminating media from escaping from the confined work areainto the surrounding atmosphere. In short, it is desirable to controlthe airborne contamination in a biological work environment by bothpreventing the ambient aerosols from contaminating a work sample andalso preventing contaminating aerosols from escaping from the worksample into the surrounding environment.

A suggested method for accomplishing these objectives is to provide acabinet to generally contain a work area and the work sample thereinwhile providing an access means for a workman to handle the work sample.Simultaneously, a laminar flow environment is provided in the cabinet toprovide an air curtain over the access means to prevent cross flow ofaerosols between the work area and the exterior of the cabinet.

It is naturally advantageous to provide the most efficient means ofinsuring that no cross contamination occurs and by providing closecontrol over the laminar flow air barrier provided by the cabinetarrangement. Therefore. control means which facilitates the control ofthe flow and the particular atmosphere and pressure within acontamination control cabinet would also be extremely advantageousto theart.

Naturally, the best possible protection and the most efficient andaccurate working conditions should be provided when working in thepresence of possible contamination produced by air flow. An apparatuswhich provides close control over the laminar flow of air in abiological contamination control cabinet so that the most uniform andpositive protection is achieved during the greatest percentage of thework time is desirable. At the same time the ease of acce'ssand handlingof the work sample should not be lessened thereby pro viding thegreatest protection and most efficient working conditions while handlinga sample subject to emanation or reception of ambient aerosols duringhandling thereof.

SUMMARY OF THE INVENTION With the above comments in mind, among theprimary objectives of this invention is to provide a biologicalcontamination control cabinet for controlling airborne contamination ina biological work environment. The cabinet and the apparatus associatedtherewith provide a filtered air barrier to prevent ambient aero' solsfrom'contaminating the work sample contained within the cabinet and alsoprovides a filtered air curtain over the access opening of the cabinetto prevent ambient aerosols from leaving or entering the cabinet itself.

Furthermore, a negative pressure is provided in the cabinet to preventcontamination from the work samplefrom escaping into the surroundingenvironment through the access opening in the cabinet or through anyother portion of the cabinet'where leakage might occur. All airrecirculated through the cabinet and exhausted from the cabinet by theapparatus in general is filtered by absolute filters or, as commonlydesignated in the trade by HEPA filters, to remove contaminatingaerosols. I

The apparatus provide a high velocity clean air curtain across the frontopening which provides a kinetic air barrier between the inside andoutside of the access opening in the cabinet front of the apparatus.Furthermore, all air-plenums containing contaminating aerosols are at anegative pressure with respect to the surrounding environment orcompletely contained within a surrounding negative pressure region. Thuspreventi-ng leakage of contaminated air out into the laboratory.

Cooperating with the contamination control cabinet as part of theapparatus is a device which indicates the air velocity within thelaminar flow cabinet by means of a pitot tube, or similar device,located the blower discharge within the cabinet and connecteddifferentially across a sensitive flow meter. The air velocity throughthe cabinet is indicated by calibrating the flow meter to readthe'velocity pressure in the blower'discharge against the air volumedelivered by the blower. The air velocity is controlled by means of asolid state electronic speed controller of a'common commercial type, onthe blower motor with the entire velocity indicator, speed control andswitches being incorporated into an injection molded control panel whichmay be mounted on the laminar flow cabinet. The air velocity indicatorand control indicates air velocity and is independent of static pressurewhile providing a combination velocity indicator and control which isincorporated as a one-piece. unit adapted to be mounted on thecontamination control cabinetwith easy access and 0perability availableto a person working with the contamination control apparatus in general.

In this manner, close control may be maintained at all times over theenvironment contained within the work area in which the work sample islocated thereby providing an'effective and efficient contaminationcontrol apparatus which is a significant improvement over the known art.a a I Briefly, the contamination control apparatus of this inventionincludes a hollow cabinet having a work area in one portion thereof andan opening therein permittingaccess to the work area from the exterior.of the cabinet. Decontamination and air supply means are in the cabinetand positioned so that air discharge there.- from will be decontaminatedand then passed into the work area. Diffusion means are mounted in thecabinet and positioned between the decontamination and supply means andthe work'area to facilitate the diffusion of the air as it enters thework area. Consequently, the

air flows uniformly through the work area and assists in providing aclean air curtain over the access opening to through the access opening.A series of interconnected air plenum chambers are in the cabinet incommunication with the work area, decontamination and air supply means,and the opening to the exterior of the cabinet to permit the air passingthrough the work area and a portion of air from outside of the cabinetto be directed to the decontamination and air supply means. Negativepressure reducing means are in the cabinet to direct a predeterminedamount of decontaminated air out of the cabinet sufficient to maintain alesser pressure within the cabinet and exteriorly thereof and, finally,air velocity indicator and control means are mounted on .the cabinet tofacilitate the control of air flow within the cabinet.

'BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is aperspective view of a contamination control apparatus of this invention;

FIG. 2 is a side elevation view thereof with the frontpanels and baseportions having beenremoved;

- FIG. 3 is a sectional end elevation view thereof taken along the planeof line 33-of FIG. 2 with arrows showing the direction of air flowwithin the apparatus;

FIG. 4 is a schematic wiring diagram of the electrical systemincorporated in the apparatus of this invention;

DESCRIPTION OF THE PREFERRED EMBODIMENT Initially, referenceshould bemade t e-FIGS. 1-3 I which depict the entire contamination controlapparatus .20 in assembled and operational condition. As

shown in F lG. l, the apparatus consists of a cabinet 21 i and aremovable floor stand 22. The removable floor stand is usable tofacilitate bringing cabinet 21 to a more comfortable working level forthe'operator. A glove port panel 23 is provided on the exterior ofcabinet '21 with two glove ports 24 and 25 provided therein tofacilitate reception of the hands of the operator when he is working ona work sample within cabinet 21. The glove port panel may be fastened byany common fastening means such as the thumb screws 26 shown in FIG. I.A portion of the front side of cabinet 21 is constructed of atransparent material such as glass. This portion 27 facilitates viewingof the interior of the cabinet 2] during operation. It might also benoted that the front portion of the cabinet which in cludes transparentportion 27 and glove port panel 23 is tapered outwardly from top tobottom with respect to the cabinet thereby providing a greater work areawithin the cabinet on which to rest the work element such as horizontalsurface or work deck 28.

The velocity indicator and control panel 29 is located i i on the frontside of cabinet 21 above transparent portion 27. The upper outer frontportion ofv cabinet 21 contains a removable panel 30 which when removedpermits access to the interior of the cabinet in the area where theblowers are located. This facilitates maintenance of the workingcomponents of the apparatus. Once again, removable panel 30 is fastenedin position by any common means such as thumb screws 31.

Cabinet 21 itself takes a substantially rectangular configuration withthe exception of the outwardly extending portion of the front side whichwas discussed above. The remainder of the cabinet is completely enclosedand includes a top panel 32, a rear panel 33, opposing sidepanels 34'and 35 and base panel 36. If the removable floor stand is employed, itis designed to mate with the bottom surface of bottom panel 36 so as tomaintain cabinet 21 in an upright supported position.

Also to be noted in FIG. 1 in viewing the top panel 32, a protectivescreen 37 is present through which the exhaust air is expelled from thecabinet in a manner which will be explained in greater detail below.Also present on the top panel 32 is a make-up prefilter 38 and aslidablemake-up prefilter damper 39 to close make up prefilter 38 whenit is not desirable to utilize this element. The make-up prefilter isutilized primarily only in facilitating initiation of operation ofapparatus 20 and thereafter damper 39 is in the closed position.Theexhaust protective screen is necessary to provide the exhaust outletfor the exhaust blower as will be described in detail below.

Turning to FIG. 2 in particular, it will be noted that in this Figurethe front panels of cabinet 21 have been removed and the interior ofcabinet 21 as seen from the front view without the presence of removablepanels is shown. On the lower portion of cabinet 21, a rear exhaustscreen 40 is shown mounted to back panel 33 of the cabinet. The entireaccess opening 41 is exposed one glove port panel 23 has been removed.Gas air or water cocks 42 may be provided for the introduction ofwhatever fluid is desirable for a particular use to which the cabinet isto be put. Furthermore, adjacent thereto at the lower portion of thecabinet is a standard outlet 43 to which proper electrical connectionsfor the system may be attached.

Velocity indicator and control panel 29 is mounted on thepermanentportion of the front side of cabinet 21 and noted thereon is thevariableair velocity control knob 44 as well as an off-on switch 45 to turn theblowers olf and on and a light switch 46 to turn the lights within theunit off and on as .will'be described in detail below. Also on controlpanel 29 is the velocity indicator 47 shown in connection with the airsupply blower 58 exposed with the removal of upper front panel 30 fromcabinet 21. The particular elements of control panel 29 will bedescribed in detail at a later point in this disclosure; It may be notedthat an input hose 49 forair is connected between the blower 48 and thelower end of velocity indicator or flow meter 47 and a correspondingoutput line 50 is also connected between air supply blower 48 and theupper end of flow meter 47 to return the air to the blower exhaust whenit has passed through flow' meter 47.

within the cabinet. Suitable mounting shelves are shown in the drawingsin particular in FIG. 2.

All of the filters employed with the apparatus of this invention arefilters which are generally known in the art as absolute filters whichprevents the transferring of contamination along with air flow into andout of the cabinet. A designation well known in the art for a filterwhich will work satisfactorily with a cabinet of this type is a filterknown as an HEPA filter which will achieve the desired results duringthe operation of the apparatus 20.

Mounted adjacent to air supply blower 48 within the upper portion ofcabinet 21 is exhaust blower 53 which is also suitably mounted withinthe cabinet by means of any convenient means such as the shelving andbracketing shown in FIG. 2. The exhaust end of exhaust blower 53 isconnected to exhaust filter 54 which is also an absolute filter of theHEPA type as mentioned above. The upper end of exhaust filter 54communicates with screen 37 and therethrough to the atmo- ,20 sphere outof cabinet 21. Exhaust filter 54 is mounted within cabinet 21, as shown,in an enclosed arrangement so that the only communication with screen 37i and the exterior of the cabinet is by passage through filter 54.Consequently, all air exhausted through exhaust blower 53 passesthrough'filter54 and in this manner contaminating aerosols are filteredout and prevented from leaving the cabinet through the opening in whichscreen 37 is mounted.

The remaining elements of the interior apparatus of the cabinet whichare subject to air flow within the cabinet are depicted most clearly inFIG. 3 of the drawings. A description of the flow patterns of the airwithin the cabinet would be an effective way to describe the cooperationbetween the various portions of the cabinet structure. To initiateoperation of the laminar flow cabinet. switches 45 and 46'are initiatedto turn on the lights within cabinet 21 and air supply blower 48respectively. The lights are located in the upper forward portion of thework area and mounted to the cabinet walls. Two conventional whitelights 55 and 56 are located adjacent an ultraviolet light 57. As willbe described in connection with the wiring diagram of the electricalsystem of the apparatus 20, either the'conventional lighting or the'ultraviolet lighting may be utilized as desired.

Air supply blower 48 then discharges a volume of air into dischargechamber 58 where it passes through air supply filter 51. Air chamber 58and air supply filter 51 are confined in bracketing within the cabinet21. The clean filtered air from filter 51 then passes through openingsin the bracketing at the lower side of the filter 51 into a plenumchamber 59 from where it'continues its downward flow through diffusionscreen 60. Diffusion screen 60 is mounted to two opposing substantiallyvertical bracket platesmounted within the cabinet and horizontallybridges the two vertical plates at a point adjacent the upper endsthereof. Screen 60 forms a diffusion means for forming uniform laminarflow of the air as it passes therethrough and continues on down throughwork area 52. Screen 60 is constructed so that a laminar flow transferof air is accomplished between plenum 59 and work area 52.

The uniform flow of air downward through work area 52 and over the worksurface protects the work sample located within work area 52 fromexternal airborne contamination. A horizontal deck 28 is located at thebase of work area 52 and forms a working surface. Deck 28 may be formedof a formica material or any other common working surface for anapparatus of this type. The two previously mentioned vertical plates 61and 62 along with deck 28 and screen form substantially the entireconfining dimensions of the work area 52 particularly when taken incombination with side panels 34 and 35 of cabinet 21 itself.

There are three potential exits points from work area 52 for thedownwardly flowing air through the work area. These are through thefront access opening 41 previously discussed and through bottom returnscreen 63,0r rear return screen 40. In actual operation as will bediscussed in greater detail at a later point in the disclosure, the airpassing through work area 52 is prevented from exiting through accessopening 41 by means of an air curtain formed across this opening.Therefore all of the air passing through screen 60 and downward throughwork area 52 must exit the work area through bottom return screen 63 andrear return screen 40. Therefore, contamination generated by the worksample itself is picked up by the clean airflow passingvdownwardlythrough work area 52 and swept out of the work area through returnscreens 63 and 40.

The nature of the confining internal support structure within thecabinet to form work area 52, plenum 59, filter 51 and air chamber 58 isall support structure which is mounted in a conventional manner to theinterior framework of the cabinet and also serves to form a series ofinterconnected plenum chambers between this confining structure and theinterior surface of the outer confining walls of cabinet 21. Thisinterconnected plenum system consists of plenum 65 adjacent the bottomof cabinet 21 which communicates with vertical rear plenum 66 which inturn communicates with upper plenum 67. Therefore, contaminated airpassing through screen 63 and 40 is picked up in plenums 65 and 66 andreturned to air supply blower 48 where it recirculates back through thework area after being filtered by HEPA filter 51.

Additionally, a portion of the contaminated air passing through plenum65 and 66 enters upper plenum 67 at a position where it is picked up byexhaust blower 53 and this portion of contaminated air is exhausted fromthe cabinet through filter 54 and screen 37 at the top of cabinet 21.This portion of air is clean since the contaminated aerosols containedtherein are removed by filter 54. In turn, this clean exhausted airwhich passes through screen 37 causes a negative pressure within cabinet21, particularly in the areas defined by plenums 65, 66 and 67. Thisprevents contaminated air contained within these plenums from escapingthrough any construction I joint leaks which might exist in the outercabinet wall construction into the laboratory. The slightnegativepressure is sufficient to assure that the outside atmospheric pressurepresents any air from the inside of the cabinet 21 which is contained inareas such as plenum 65, 66 and 67 from escaping the interior of thecabinet. This is a particular advantageous feature because these plenumsgenerally contain contami nating aerosols which should not be allowed toescape.

from the interior of the cabinet. All air which is permitted to escapefrom-the cabinet passes through an HEPA filter before it is allowed topass therefrom.

As shown by the arrows, in order to maintain equilibrium within thecabinet 21 during operation of the apparatus, an equal quantity of airto that exhausted through screen 37 is made upor drawn into the cabinetthrough access opening 41 and mixes with internally contaminated airpassing out of work area 52 through screen 63 and into plenum chamber65. Additionally, screen 60-creates a slight pressure in plenum area 59and causes a higher air flow velocity through slot 68 provided betweenplate 62 and transparent Outer surface 27 on the front of the cabinet.This slightly increased higher air flow velocity passing slot 68provides a curtain across access opening 41 as it extends out of thebottom of slot 68 and continues downwardly through screen 63 into returnplenum chamber 65 at the bottom of cabinet 21.

The isolation between the air inside and outside of cabinet 21 acrossfront access opening 41 is accomplished by three adjacent sheets ofdownwardly flowing air. .These sheets of air are substantiallyp'aralleland provide a triple thickness curtain to assure that no contaminationcan pass between work area 52 and the exterior ofcabinet 21. This triplecurtain is formed by the I air being drawn into the cabinet by reason ofthe nega tive pressure condition within-the cabinet, the high ve locityair passing downward through slot 68 which is sandwiched between theoutside air being'drawn in'and the laminar flow clean air passingdownwardly through work area 52 from air supply blower 48. Contaminatedair from inside of the cabinet 21 is drawn into the inner edge of bottomscreen 63 and therefore all of the contaminated air from inside thecabinet passes into plenum 65 and contaminated air from outside thecabinet is drawn into the outer edge of bottom return screen 63 as shownby the arrows in FIG. 3. Thus, all of the contaminat'ed air from outsideof the cabinet passes into plenum chamber 65 and does not reach workarea 52 in contaminated condition. The high velocity air curtainextending downwardly from slot 68 positively 'sep-' arates these twocontaminated flows and creates an additional positive kinetic barrier.Thus, for air to move from inside of the cabinet out or from outsidein,-it must in effect cross three air streams. The resultant cabinet 21in operation .provides a filtered air barrier opening 70, and lightoff-on switch 46 is mounted in opening 71. An external knob 72 isprovided to rotate variable speed control 44 to vary the blower speedand knob 72 and control 44 are mounted by any convenient means such aslock nut 73 as shownin F IG. 5. Suitable electrical terminals are shownon variable controller 44 as well as on switches 45 and 46. A mountingbracket 74 is also provided to assure that blower variable control 44 ismounted in the most desirable fashion.

Turning to consideration of the flow meter 47, FIGS. 5 and 6 should beconsidered together. The internal chamber of flow meter 47 is formed inpanel 29 and has a tapered frusto conical configuration which is of awider diameter at the upper end thereof than at the lower end thereof.This chamber 55 is initially open at the upper and lower ends thereof,howeverplug 76 and 77 are fitted to suitable recesses in the upper andlower end of chamber 75 so that the ends thereof are sealed prior tooperation of the apparatus.

Extending from the rear of panel 29 are tubular extensions 78 and 79 invertical arrangement so that tubular extension 78 extends horizontally.from a position adjacent the upper portion of'pan el 29 and tubularextension 79 extends horizontally in substantially the same verticalplane from a position adjacent the lower portion of panel 29. A bore 80extends through tubular extension 78 and through panel 29 intocommunication with chamber 75 in a substantially perpendicularrelationship therewith. Similarly, a bore 81 extends through tubularsection 79 and throughpanel 29 into communication with the lower portionof chamber 75 also at substantially a perpendicular relationship withrespect thereto. Tube 49 has one end mounted-in any convenient mannerwithin tubularext'ension 79 so that the passage therethroughcommunicates withbore 81 and the lower end of chamber 75. Similarly, oneend of tube 50 is conveniently mounted within tubular extenacross accessopening 41 which prevents ambient aerosols from contaminating the worksample in work area 52 and also provides afiltered air curtain andfanegative pressure within the cabinet to prevent contamination from thework sample from escaping into the surrounding environment. All airrecirculated through the cabinet and exhausted from the cabinetis'filtered by HEPA filters to remove contaminating aerosols. Naturally,theair curtain across access opening 41 in no way interferes with anoperator working on 'a work sample contained within working area 52.Only a kinetic air barrier seals access 41 and prevents cross flow ofair between the inside and outside of the cabinet.

Turning to consideration of the controls employed in operating theapparatus 20 of this invention, FIGS. 5 and 6 best depict thesefeatures. The support panel 29 itself which is mounted on the front wallof cabinet 21 is of one-piece integral construction and contains a flowmeter 47 therein and openings therethrough in. which to mount thevariable velocity control 44, the

off-on switch for the air blowers, and the off-on switch for the lightscontained within the cabinet. These openings are designated by thenumeral 69, 70 and7l respectively in FIG. 5. Variable control 44 ismounted in opening 69, air blower off-on switch 45 is mounted in sion 78and the passage therethrough communicates with bore 80 and the upperportion of chamber 75. As

previously discussed, the opposite endsof tubes 49 and a 50 are mountedto the blower discharge portion of air supply blower 48 so that aportion of tubes 49 and 50 extend within blower 48 in the air dischargeportion thereof. Convenient sealing gaskets 82 and 83 may be employed toinsure that no air escapes at the point where tubes 49 and 50 enter theair exhaust portion of air supply blower'48.-Ga'sket 82 assists insealing the entrance of tube 49 and gasket 83 assist in sealing theentrance of tube 50 into air supply blower 48.

Positioned within chamber 75 of flow meter 47 is a movable indicator 84which is free to move vertically within chamber 75. Movable member 84may take any convenientform such as a ball shaped as shown in FIG. 6 andmay be formed of any convenient material such as nylon. If it isdesirable for any reason to remove or replace indicator 84 forcalibration purposes or other reasons, a transverse passage 85 islocated adjacent the The ends of tubes 49 and 50 contained within blower48 are sealed by plugs 86 and 87 respectively. A plurality of spacedopenings 88 are located in tube 49 along the portion thereof containedwithin blower 48 and face the direction from which air is beingdischarged from the blower. Therefore, air will enter openings 88 andpass through tube 49. Correspondingly, tube 50 has a plurality of spacedopenings 89 located on its surface on the portion thereof which isinside of blower 48 and these openings face the direction in which airis being discharged from air supply blower 48. This is depicted by thearrows in FIG. 6. Therefore, air passing through tube 50 will exitthrough openings 89 into the discharge portion of air supply blower 48.

The above arrangement of openings facilitates operation of flow meter47. As air is discharged from air supply blower 48, it will enteropenings 88 in tube 49 and pass therethrough into the lower end ofchamber 75. The air will pass upward through chamber 75 and exit throughpassage 80 into tube 50. It will pass through tube 50 and exit throughopenings 89 back into the discharge portion of air supply blower 58 andsubsequently exit therefrom. The arrangement of openings within thedischarge portion of air supply blower 48 may take the arrangement as isused in a common air velocity indicating device known in the art as apitot tube. The force with which the air passes through chamber 75 willdetermine the height to which indica tor 84 is driven upward withinchamber 75. The height at which indicator 84 is located is read inaccordance with a calibration marking on the transparent outer surfaceof flow meter 47. Therefore, if a marked change in the height ofindicator 84 is-noted, a subsequent change in the speed at which theblower discharges air may be made by adjusting variable speed controller44. This is accomplished as discussed above by merely turning knob 72 oncontrol panel 29.

Thus, a device is provided which indicates the velocity within thecabinet 21 by means of a pitot tube or similar device located in theblower discharge and connected differentially across a sensitive flowmeter. Air velocity through the cabinet is indicated by calibrating theflow meter to read the velocity pressure in the blower discharge versusthe air volume delivered by the blower. Air velocity is controlled bymeans of a speed controller. which may be of the solid state electronictype commonly known in the art,'located on the blower motor. The entirevelocity indicator, speed control variation mechanism and switches foroperation of apparatus 20 are incorporated into a single control panel.Control panel 29 may be conveniently injection molded of a commonplastic material if desired. The control panel indicates air velocityand is independent of static pressure and the entire velocity indicatorand control system is incorporated into a one-piece construction.Naturally if it is desirable to change the calibration, it may beaccomplished in many ways one of which would be to change the diameter,weight or configuration of indicator 84.

Finally, consideration should be given to a suggested wiring arrangementwhich may be utilized with the apparatus of this invention such as theschematic arrangement shown in FIG. 4 of the drawings. A normal 120 voltsystem may be employed as indicated by leads 90 and 91 with a separateground utilized as indicated by ground 92. The blower switch 45 isconnected to the blower portionof the circuit and the light switch 46 isof the type which may be in an off position or which may be connected inone of two on positions. In one on position it would provide a closecircuit to light two common types of white light devices such as commoncommercial neon lights as indicated by the reference numerals 55 and 56.Alternatively in the other on position it may be connected to form aclose circuit with a common type of ultraviolet light as indicated bythe reference numberal 57 in the drawings. A circuit containing switch46 and lights 55 and 56 will generally also contain a ballast means 93for use with the conventional neon or fluorescent lights 55 and 56.Similarly, when switch 46 is connected so as to close the circuit withultraviolet light 57 to permit current to flow along that particularpath, a transformer means 94 is included in the circuit as isconventionally done in accordance with the use of a commonly usedultraviolet light such as designated by the reference numeral 57. Asshown in the drawings, the light circuit is such that the fluorescentlights are lit as current flows through the circuit formed by lead90,-switch 46, lights 55 and 56, ballast 93 and lead 91 and theultraviolet light is lit when current flows through the circuit formedby lead 90, switch 46, light 57, transformer 94 and lead 91.

As shown in FIG. 4, switch 45 for initiating operation of air supplyblower motor 48 and exhaust motor 53 is in the open position so that theapparatus of the invention is not in operable position. Upon the closingof switch 45, current will flow through lead 90, switch 45 and therespective motors of air supply blower 48 and exhaust blower 53, andlead 91. lt should be noted that each of the blower motors areindividually grounded and a capacitor is connected to the motor of theair supply blower 48 to prevent any premature surge of power to thatmotor which could cause an undesirable static discharge inthe'electrical system. Variable speed controller 44 is shown connectedto both the motor of the air supply blower and the exhaust blower. Thisis to assure that a uniform amount of air is constantly being circulatedthrough cabinet 21. A variation in speed of the motor of air supplyblower 48 should be accompanied by a proportional variation and speed inthe motor of exhaust blower 53. This assures that a constant volume ofair is being circulated through cabinet 21 and that the slight negativepressure is maintained at all times within the cabinet to prevent thecross contamination as discussed in detail above.

Thus, the above objectives of the invention, among others, areeffectively attained.

I claim: v

1. A contamination-control apparatus comprising:

a hollow cabinet having a work surface mounted in one portion thereofand an opening in the front wall of the cabinet permitting access andbeing adjacent to a portion of the work surface;

air supply means mounted in said cabinet;

high efficiency filter means mounted in said cabinet and connected tothe air supply means by a plenum and positioned so that air dischargefrom said air supply means passes therethrough for decontamination anddiffusion of the air;

diffusion means mounted in the cabinet between the high efficiencyfilter means and the work surface for diffusion as air enters the workarea so that laminar flow is provided on the work surface and projacentthe access opening and adjacent the difiusion means for communicationwith flow from the filter for directing a predetermined portion of thefilter air discharge from the air supply means across the access openingat a higher velocity than the air passing through the diffusion meansand to thereby form an air curtain across the access opening within thecabinet and prevent interchangeability of air between the work area andthe exterior of the cabinet; exhaust means from said cabinetcommunicating with said work surface to direct a predetermined amount ofair from said cabinet; said exhaust means including negative pressureproducing means sufficient to maintain a lesser pressure within aportion of said cabinet than exteriorly thereof; said exhaust meansincluding air direction means within said cabinet to direct the flow ofair there'- throughwith only a negative pressure condition present inthat portion of the cabinet adjacent to the exterior walls thereofto-minimize the danger of leakage of air from the interior of thecabinet: and

tate the direction of air flow with respect to the interior of saidcabinet.

3. The invention in accordance with claim 1 wherein said air supplymeans includes an air supply blower mounted in said cabinet andpositioned so that air discharge therefrom will be directed into saidwork area, and said exhaust means including an exhaust blower mounted insaid cabinet and in communication with the exterior of said cabinet todirect a predetermined amount of air out of said cabinet, and an exhaustfilter mounted in said cabinet between the exhaust blower and theexterior of said cabinet to assure that only clean air is removed fromthe exterior of said cabinet.

4. The invention in accordance with claim 1 wherein said work surfaceincludes the zone defined by a horizontal table and at least twosubstantially vertical plates spaced from oneanother and spaced abovesaid table to permit removal of air from said work surface.

5. The invention in accordance with claim 1 wherein said diffusion meansis a screen forming a substantial portion of the upper boundary of thework area and is positioned with respect to said filter means and airsupply means so that a substantial portion of the air supply therefrompasses through said screen.

6. The invention in accordance with claim 1 wherein said channelmeansincludes two substantially vertical plates in said cabinet adjacent tosaidwork area and terminating above said access opening with the channelformed between said plates communicating at one end with the exhaustside of said filter and at the other end with the access opening so thata portion of the air exhausted from said filter passes at a relativelyhigh velocity through said channel and across said access opening toprovide an air curtain.

7. The invention in accordance with claim 1 wherein air velocityindicator means are mounted on said cabinet to monitor the air velocityin said cabinet.

8. The invention in accordance with claim 7 wherein control means are onsaid cabinet in connection with said air supply means to facilitate theadjustment of air flow within said cabinet in response to an indicationof said air velocity indicator.

1. A contamination control apparatus comprising: a hollow cabinet havinga work surface mounted in one portion thereof and an opening in thefront wall of the cabinet permitting access and being adjacent to aportion of the work surface; air supply means mounted in said cabinet;high efficiency filter means mounted in said cabinet and connected tothe air supply means by a plenum and positioned so that air dischargefrom said air supply means passes therethrough for decontamination anddiffusion of the air; diffusion means mounted in the cabinet between thehigh efficiency filter means and the work surface for diffusion as airenters the work area so that laminar flow is provided on the worksurface and providing a controlled flow passage for a substantialportion of the air from the air supply means to the work surface; meansdefining a channel mounted in said cabinet adjacent the access openingand adjacent the diffusion means for communication with flow from thefilter for directing a predetermined portion of the filter air dischargefrom the air supply means across the access opening at a higher velocitythan the air passing through the diffusion means and to thereby form anair curtain across the access opening within the cabinet and preventinterchangeability of air between the work area and the exterior of thecabinet; exhaust means from said cabinet communicating with said worksurface to direct a predetermined amount of air from said cabinet; saidexhaust means including negative pressure producing means sufficient tomaintain a lesser pressure within a portion of said cabinet thanexteriorly thereof; said exhaust means including air direction meanswithin said cabinet to direct the flow of air therethrough with only anegative pressure condition present in that portion of the cabinetadjacent to the exterior walls thereof to minimize the danger of leakageof air from the interior of the cabinet; and means for directing aportion of the air from the work surface to the air supply blower. 2.The invention in accordance with claim 1 wherein a series ofinterconnected air plenum chambers are in said cabinet in communicationwith said work surface, said filter and diffusion means, said air supplymeans, said access opening, and said exhaust means, to facilitate thedirection of air flow with respect to the interior of said cabinet. 3.The invention in accordance with claim 1 wherein said air supply meansincludes an air supply blower mounted in said cabinet and positioned sothat air discharge therefrom will be directed into said work area, andsaid exhaust means including an exhaust blower mounted in said cabinetand in communication with the exterior of said cabinet to direct apredetermined amount of air out of said cabinet, and an exhaust filtermounted in said cabinet between the exhaust blower and the exterior ofsaid cabinet to assure that only clean air is removed from the exteriorof said cabinet.
 4. The invention in accordance with claim 1 whereinsaid work surface includes the zone defined by a horizontal table and atleast two substantially vertical plates spaced from one another andspaced above said table to permit removal of air from said work surface.5. The invention in accordance with claim 1 wherein said diffusion meansis a screen forming a substantial portion of the upper boundary of thework area and is positioned with respect to said filter means and airsupply means so that a substantial portion of the air supply therefrompasses through said screen.
 6. The invention in accordance with claim 1wherein said channel means includes two substantially vertical plates insaid cabinet adjacent to said work area and terminating above saidaccess opening with the channel formed between said plates communicatingat one end with the exhaust side of said filter and at the other endwith the access opening so that a portion of the air exhausted from saidfilter passes at a relativEly high velocity through said channel andacross said access opening to provide an air curtain.
 7. The inventionin accordance with claim 1 wherein air velocity indicator means aremounted on said cabinet to monitor the air velocity in said cabinet. 8.The invention in accordance with claim 7 wherein control means are onsaid cabinet in connection with said air supply means to facilitate theadjustment of air flow within said cabinet in response to an indicationof said air velocity indicator.